The use of organometallic compounds having two ligands which are or contain the cyclopentadienyl anion as catalysts for the polymerization of olefinic and/or diolefinic compounds is already known (sandwich metallocenes, see EP 35,242, EP 69,951, EP 129,368, EP 277,003, EP 277,004).
It is also known to use organometallic compounds having only one cyclopentadienyl anion as catalysts (semi-sandwich catalysts, see U.S. Pat. No. 5,132,380, EP 416,815, WO 91/04257, WO 96/13529). Semi-sandwich catalysts having an indenyl ligand bridged in the 2-position have not hitherto been known.
Biscyclopentadienyl metal complexes that have a bridge between the two cyclopentadienyl ligands are called ansa-metallocenes. The particular metallocenes include the bisindenyl metallocenes bridged in the 1-position on the indenyl ligand. Such chiral ansa-metallocene derivatives are especially suitable as catalysts for the preparation of olefin polymers having a high degree of isotaxy, a narrow molecular mass distribution and a high molecular mass, as is described, for example, in EP 485,821 and EP 485,823.
Comparatively little is known about metallocenes having indenyl ligands bridged in the 2-position. Organometallics 1997, 16, 3044-3050 describes an ansa-bisindenylhafnium complex in which one of the indenyl ligands is bridged in the 2-position (dimethylsilyl-(1-indenyl)(2-indenyl)-bis-dimethylamidohafniium, further reaction to dimethylsilyl-(1-indenyl)(2-indenyl)-dimethylhafnium). The metal complex is formed as a by-product in a low yield in a specific process (vacuum, 160.degree. C.) and must be purified in a complicated process. In Organometallics 1993, 12, 5012-5015, a multi-step method of synthesizing ethylenebis(2-indenyl)-titanium dichloride is described. On account of the multi-step synthesis and the numerous purification operations, the yield that can be achieved is very low. Owing to the method of synthesis, the structural variety is restricted to ethylene-bridged ligands. WO 94/11406 discloses organometallic compounds of transition metals which have an indenyl ligand and a cyclopentadienyl ligand, the indenyl ligand being substituted in the 2-position; that substituent may also be in the form of a bridge to the second ligand. The Examples show multi-step preparations with extremely unsatisfactory yields which, in the case of bridged compounds, lead to 1-cyclo-pentadienyl-2-(2-indenyl)-ethane-zirconium chloride, to bis-(2-indenyl)-methane-zirconium dichloride or to dimethylbis-(2-indenyl)-silane-zirconium dichloride, which still contains impurities. In EP 372,414, the two compounds ethylene-1-((3-but-3-enyl)inden-1-yl)-2-((1-but-3-enyl)-inden-2-yl)zirconi um dichloride and ethylene-1-((3-allyldimethylsilyl)-inden-1-yl)-2-((1-allyldimethylsilyl)-i nden-2-yl)zirconium dichloride are mentioned.
Owing to the poor availability of organometallic compounds of transition metals having an indenyl ligand bridged in the 2-position, little is known about their use or their catalytic activity.